GIFT  OF 


J 


No.  1814 


DESCRIPTION  AND  INSTRUCTIONS 
FOR  CARE  AND  OPERATION 


OF 


FIRING  MAGNETOS 

TYPES  GA  AND  MA 


(TWO  PLATES) 


MARCH  10,  1917 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1917 


No.  1814 


DESCRIPTION  AND  INSTRUCTIONS 
FOR  CARE  AND  OPERATION 

OF 

FIRING  MAGNETOS 

TYPES  GA  AND  MA 


(TWO  PLATES) 


MARCH  10,  1917 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1917 


c. 


Wab  Department, 
Office  of  the  Chief  of  Ordnance, 

Washington,  March  10,  1917* 
Tliia  manual  ia  published  for  the  information  and  government  of  the  Regular  Army 
and  National  Guard  of  the  United  States. 
By  order  of  the  Secretary  of  War: 

William  Crozier, 
Brigadier  General,  Chief  of  Ordnance. 
10067—17  C3  > 


365263 


Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

IVIicrosoft  Corporation 


http://www.archive.org/details/careoperationOOunitrich 


DESCRIPTION  AND  INSTRUCTIONS  FOR  THE  CARE  AND 
OPERATION  OF  FIRING  MAGNETOS. 


1 .  The  firing  magnetos  described  below  have  been  developed  to 
replace  the  firing  pistol  and  battery  used  on  seacoast  gun  carriages 
and  the  D.  C.  magneto  used  for  firing  mortars. 

MAGNETO  TYPE  GA,  FOR  GUNS. 

(Plate  I.) 

2.  For  gun  firing,  type  GA'is  used.  This  magneto  is  designed  for 
firing  one  primer  only,  and  is  issued  for  all  guns  using  separate 
ammunition. 

3.  The  magnetos  are  numbered  serially,  the  first  100  having  a  base 
differing  slightly  from  those  of  higher  number.  Numbers  1  to  100 
have  two  threaded  lugs  on  the  base  through  which  the  old-style 
firing  cable  with  spiral  armor  passes.  By  means  of  a  gasket,  nut,  and 
sleeve,  the  cable  is  made  fast  to  the  base. 

4.  Numbers  101  and  following  have  a  single  entrance  provided  in 
the  base  for  the  twin  conductor  leaded  and  armored  firing  cable. 

5.  The  principal  parts  of  this  magneto  are:  Case  with  base,  firing 
lever,  lever  catch,  lever  spring,  spring  plunger  and  spring  lever, 
lever  shaft,  gear  segment,  clutch-shaft  pinion,  clutch  shaft,  clutch- 
shaft  bracket,  clutch  and  spring,  clutch-shaft  gear,  armature-shaft 
pinion,  and  magneto  proper.  The  parts  are  named  approximately 
in  their  order  in  the  train  from  lever  to  magneto. 

6.  The  firing  magneto,  complete,  weighs  33  pounds. 

7.  The  case  is  of  bronze,  and  protects  the  interior  from  dust  and 
excessive  moisture.  By  means  of  a  lug  at  the  rear  it  is  securely 
attached  to  the  bracket  provided  on  the  sight  standard. 

8.  The  firing  lever  is  heavily  constructed  to  resist  bending  under 
excessive  strain.  It  is  held  in  the  locked  position  by  a  catch,  and 
when  the  lever  is  gripped  preparatory  to  firing  the  catch  is  automati- 
cally released.  The  lever  is  returned  to  the  locked  position  by  the 
lever  spring,  assisted  by  the  weight  of  the  lever  itself.  It  has  been 
found  that  it  is  not  necessary  to  raise  the  lever  violently,  as  even  a 
small  and  slow  movement  will  fire  a  primer.  The  gear  ratio  is  such 
that  one  complete  revolution  of  the  lever  would  give  48  revolutions 
of  the  armature.     As  the  lever  can  be  easily  moved  at  the  rate  of  one 

(5) 


T  «  c^  ^  c 


6 


turn  in  a  second,  it  is  seen  that  very  high  armature  speeds  may  be 
obtained.  When  the  lever  is  raised,  the  gear  segment  on  the  far  end 
of  the  lever  shaft  turns  the  combination  pinion  and  clutch.  The 
latter,  through  the  clutch  sleeve,  turns  the  clutch  shaft  and  the  large 
gear  on  the  other  end  of  this  shaft  meshing  with  the  pinion  on  the 
armature  shaft.  The  pinion  on  the  clutch  shaft  is  extended  through 
the  clutch  shaft  bearing  and  has  on  its  inner  end  ratchet  teeth. 
These  are  normally  in  mesh  with  the  teeth  on  the  clutch  sleeve.  The 
sleeve  slides  free  on  a  flat  section  of  the  shaft,  but  must  turn  with  it, 
and  is  held  in  mesh  with  the  pinion  by  a  spring.  Thus,  when  the 
lever  is  raised,  the  armature  is  revolved,  and  when  the  lever  stops  the 
clutch  teeth  slide  over  each  other,  the  spring  allowing  the  sleeve  to 
back  off  from  engagement  with  the  pinion  clutch.  The  armature  is 
thus  allowed  to  revolve  until  its  momentum  is  lost  and  sustain  the 
current, 

9.  This  magneto  will  deliver  on  open  circuit  about  45  volts  at 
2,000  r.  p.  m.  Through  an  external  resistance  of  1  to  3  ohms,  it 
will,  at  2,000  r.  p.  m.,  generate  about  0.8  ampere  at  1  volt  pressure. 
Small  external  resistances  do  not  greatly  affect  the  output  and  a 
primer  can  be  fired  with  as  much  as  60  ohms  resistance  in  the  circuit. 
The  armature  and  brush  resistance  is  about  3  ohms. 

10.  The  average  current  being  about  0.8  ampere  it  will  be  ample 
to  fire  one  primer.  However,  the  capacity  is  in  general  not  sufficient 
to  fire  in  parallel,  since  about  0.4  ampere  or  more  is  necessary  to  fire 
a  primer.  As  the  resistance  of  the  firing  circuit  is  less  than  1  ohm  it  is 
seen  that  while  a  large  number  of  primers  might  be  fired  in  series, 
only  two  could  be  fired  in  parallel,  under  favorable  circumstances. 
The  magneto  should  not  therefore  be  expected  to  fire  more  than  one 
primer  except  in  series. 

11.  The  magneto  proper  is  made  by  the  Sumter  Telephone  Manu- 
facturing Co.,  and  is  their  type  JR.  The  armature  is  wound  with 
530  to  540  turns  of  No.  21  wire  (B.  &  S.) 

MAGNETO  TYPE  MA,  FOR  MORTARS. 
(Plate  II.) 

12.  This  magneto  is  quite  similar  in  principle  and  construction  to 
the  type  GA,  the  capacity  being  considerably  greater,  however.  It 
is  designed  to  fire  four  primers  in  parallel  and  for  this  purpose  the 
current  output  must  be  at  least  1.5  to  2.5  amperes.  In  the  branches 
of  a  divided  circuit  the  greater  portion  of  the  current  flows  in  the 
branches  of  least  resistance.  It  is  therefore  desirable  to  have  as 
great  an  output  of  current  as  practicable  in  excess  of  the  necessary 
requirement  in  order  to  insure  that  all  branches  have  the  necessary 
current.  It  is  also  very  important  that  the  resistance  in  all  branches 
be  kept  as  nearly  the  same  as  possible. 


13.  The  characteristics  of  this  magneto  are  as  follows:  The  voltage 
on  open  circuit  is  about  50  at  4,000  r.  p.  m.  Through  an  external 
resistance  of  2  ohms  at  4,000  r.  p.  m.  the  output  is  about  8  amperes 
at  16  volts,  and  at  1,000  r.  p.  m.,  through  the  same  external  resistance, 
the  output  is  about  4.5  amperes  at  9  volts.  The  armature  and  brush 
resistance  is  0.4  ohm. 

14.  The  gear  ratios  are  such  that  one  turn  of  the  firing  lever  causes 
30  turns  of  the  armature. 

15.  It  is  expected  that  four  primers  will  fire  simultaneously  with- 
out great  effort.  In  experimental  firing,  the  primers  have  been  found 
to  explode  upon  a  very  small  and  relatively  slow  movement  of  the 
handle.  When  difficulty  is  experienced  in  firing  all  primers  simul- 
taneously, examination  should  be  made  to  ascertain  whether  the 
branches  of  the  divided  circuit  have  approximately  equal  resistances. 

16.  The  magneto,  complete,  weighs  about  86  pounds. 

17.  The  magneto  proper  is  made  by  the  Sumter  Telephone  Manu- 
facturing Co.  and  is  designated  by  them  as  type  AGD. 

18.  A  wall  bracket  is  provided  in  or  near  each  mortar  pit  for 
mounting  the  magneto,  which  is  there  attached  to  the  engineer  cables. 

CARE  OF  MAGNETOS.  ^ 

19.  The  construction  of  the  magneto  complete  is  very  simple,  and 
but  little  attention  is  required  to  keep  it  in  good  condition.  All  nuts 
are  of  the  crown  type  held  by  a  split  pin  to  avoid  unscrewing  by 
vibration.  The  studs  for  the  six  nuts  at  the  base  are  pinned  in 
position. 

20.  When  the  magneto  is  not  in  use  for  extended  periods  it  should 
be  removed  from  the  carriage,  mount,  or  emplacement,  if  practicable, 
advantage  being  taken  of  this  opportunity  to  examine  the  interior 
before  storing. 

21.  The  only  attention  required  is  examination  of  the  interior 
approximately  twice  during  the  year  to  prevent  starting  of  rust  and 
to  allow  oiling  of  gears  and  bearings.  Openings  in  the  case  for  this 
purpose  have  been  omitted  for  the  sake  of  greater  protection.  To 
examine  the  interior,  remove  the  nuts  at  the  comers  and  sides  of  the 
base.  The  base,  with  magneto  which  is  held  to  it  by  the  remainiag 
studs,  can  then  be  removed.  There  may  be  slight  binding  of  the  base 
on  the  studs  so  that  it  wiU  be  necessary  to  insert  a  thin  tool  between 
the  base  and  the  case  in  order  to  separate  them. 

22.  The  armature-shaft  bearings  are  provided  with  grease  pockets 
and  these  should  be  kept  packed  with  waste  soaked  with  light  engine 
oil. 

23.  If  difficulty  is  experienced  in  firing  primers,  it  will  probably  be 
found  that  there  is  some  irregularity  in  the  firing  circuit  or  magneto, 
and  an  examination  should  be  made,  rather  than  an  attempt  to  over- 


come  the  difficulty  by  violent  raising  of  the- lever.  The  lever  should 
be  raised  with  a  moderately  quick  action  aifd  under  proper  conditions 
a  relatively  slow  movement  will  fire  the  primer.  The  magnets  should 
not  be  removed  from  the  magneto  frame  unless  absolutely  necessary. 
To  do  so  weakens  the  field  and  decreases  the  voltage.  When  the 
magnets  are  necessarily  removed,  they  should  be  placed  with  the  ends 
on  pole  pieces. 


COVER  FOR^  FIRING  MAGNETO. 

24.  A  cotton  duck  cover  is  provided  with  each  magneto  for  pro- 
tection against  the  weather  when  not  in  use. 

TESTING  LAMP. 

25.  There  is  provided  a  testing  lamp  for  testing  out  the  gun-firing 
circuit  and  magneto.  It  consists  of  a  low-voltage  incandescent  lamp 
attached  to  a  dummy  primer.  When  this  dummy  is  inserted  in  the 
vent,  the  firing  circuit  is  closed  in  the  usual  manner.  Upon  operating 
the  magneto  the  lamp  will  glow.  If  the  circuit  is  in  good  condition 
the  lamp  will  glow  brightly,  but  the  capacity  is  such  that  a  current 
which  will  even  produce  a  duU-red  glow  will  fire  a  primer. 

List  of  parts  of  firing  magneto,  their  piece  marks,  number,  and  location. 

TYPE    GA. 


Piece     Num- 
mark.    i  ber. 


P67Q. 
P66G. 
P67P. 
P67L. 
P67S. 
P67T. 
P67X. 
P61H. 
P67A. 
P67J.. 
P67K. 
P67C. 
P67F. 
P66K. 
P80E. 
P66H. 
P80F. 
P66C. 
P66E. 
P80D. 

P66N. 
P61F. 
P67N. 
P67G. 
P66F. 
P67H. 
P67E. 


P66D. 
P67Y. 


P67B. 
P61G. 


Name  of  part. 


Base  (for  use  with  flexible  conduit) . 
Base  (for  use  with  armored  cable) . . 

Bushings 

Case 


Clutch 

Clutch  sleeve 

Clutch-shaft  bracket . 
Gaskets,  coupling. . . 

Gear 

Intermediate  shaft. . 
Key. 


Location. 


...do 

Key,  Woodruff  No.  1 

Lever 

Lever  catch 

Lever-catch  pin 

Lever-catch  spring 

Lever-return  spring 

Lever  shaft , 

Lever  stop 

Magneto,  Sumter  JR,  or  equal . 

Nameplate 

Nuts,  coupling 

Nuts,  crown 

do 

do 

do 

Pinion 

Pins,  dowel 

Pins 

do. 
Plunger  pin . 
Rivets,  countersunk. 
Screws,  filister  head. 

do. 
Segment , 
Sleeves,  conduit. 
Split  pin. 

do. 


Bottom  of  case. 

Do. 
For  base  P67Q. 
Slips  on  magneto  bracket. 
On  intermediate  shaft. 

Do. 
Secured  to  armature  yoke. 
On  conduit  sleeves. 
On  intermediate  shaft. 
In  clutch-shaft  bracket. 
Intermediate  shaft. 
Lever  shaft. 
Armature  shaft. 
On  end  of  lever  shaft. 
On  lever. 

Lever  catch  to  lever. 
Riveted  to  lever  catch. 
Around  spring  plunger. 
In  bearings  in  case. 
Riveted  to  lever  catoh. 
Secured  to  base  of  case. 
On  front  of  case. 
Screw  on  bosses  on  base. 
For  studs  P67M;. 

On  clutch  end  of  intermediate  shaft. 
On  end  of  lever  shaft. 
On  gear  end  of  intermediate  shaft. 
On  end  of  armature  shaft. 
In  bottom  of  case  for  base. 
For  studs  P67M;. 
For  studs  P66P. 

Connects  spring  plunger  and  spring  lever. 
For  fastening  spring  to  lever  catch. 
For  fastening  clutch  shaft  bracket. 
For  nameplate. 
On  intermediate  shaft. 
In  coupling  nuts. 
For  plunger  pin. 
For  lever-catch  pin. 


List  of  parts  of  firing  magneto,  their  piece  marks,  number,  and  location — Continued. 

TYPE    GA— Continued. 


Piece 
mark. 

Num- 
ber. 

Name  of  part. 

Location. 

P61G 

Split  pin    ..      .             

For  nut  P67H. 

For  nut  P67G. 

P67U 

Spring  clutch            .... 

On  intermediate  shaft 

P66A 

Spring  lever  .            

Do. 

P66B     . 

Soring  nlunger 

Between  spring  lever  and  lug  on  case. 
Fasten  base  to  case. 

P67M 

Studs 

P66P 

..do                                   .           ..  . 

To  hold  magneto  to  base. 
On  lever-catch  pin. 
On  intermediate  shaft. 

P66J 

Washer 

P67W.... 

Washer,  clutch 

P67D 

Washer 

Do. 

TYPE     MA. 


P74B 

1 

1 

4 
1 

Base                                            ..  . 

Bolted  to  bottom  of  case. 

P74A 

Case 

Slips  on  magneto  bracket. 
On  intermediate  shaft. 

P76R 

Clutch 

P76K 

Clutch  sleeve    

Do. 

P76L 

Clutch  spring > 

Do. 

T97P 

Conductor  terminal 

Attaches  to  terminal  end  bracket. 

T97Q 

P76M 

do 

Dowel  pins 

Intermediate  gear 

Do. 
In  bottom  of  case  for  base. 
On  intermediate  shaft. 

P76F 

Intermediate  shaft 

In   terminal   end    and   pinion   end   bracket 

P75A 

Lever 

bearings. 
On  lever  shaft. 

P75E 

Lever  catch 

On  lever. 

P75G 

Lever-catch  pin 

Lever  catch  to  lever. 

P75F 

Lever-catch  spring     .        

Riveted  to  lever  catch. 

P75B 

Lever  shaft 

In  bearings  in  case. 

P75P 

Lever  stop     ... 

Riveted  to  lever  catch. 

P73E 

P73C 

Magneto,  Sumter  AGD,  or  equal 

Magneto  cable 

Bolted  to  base. 
From  plug  to  terminals. 
Connects  to  plug  box. 
On  armature  shaft. 
Do. 

P73D 

Magneto-cable  plug 

P76N 

P76P 

Magneto  pinion 

Magneto-pinion  key 

P73A 

P74G 

P74E 

P76G 

P75C 

P76H 

P73F 

P76E 

Nameplate 

Nuts,  crown 

do 

do 

do... 

do 

do 

Pins 

Pinion  end  bracket 

On  front  of  case. 

For  studs  P74C. 

For  studs  P74D. 

For  intermediate  shaft. 

For  lever  shaft. 

For  intermediate  shaft. 

For  armature  shaft. 

Secure  studs  f  P74D)  in  case. 

Secured  to  pinion  end  of  magneto. 

P73B 

Rivets 

Screws,  fllister  head. 

For  fastening  spring  to  lever  catch. 
Fasten  nameplate  to  case. 

P76D 

P76C 

P76B 

P76B 

do 

do 

do 

do 

Clamps  end  of  terminal  end  bracket. 
Conductor  terminal  to  terminal  end  bracket. 
Pinion  end  bracket  to  magneto. 
Terminal  end  bracket  to  magneto. 

P75L 

Segment 

On  intermediate  shaft. 

P75D..... 

Segment  spring ...  . 

Between  spring  hanger  and  spring  stud. 
In  lever  shaft. 

P75M 

Segment  key 

Snlitpta..                .  , 

For  lever-catch  pin. 

do 

For  spring  hanger. 
On  segment. 

P75N 

Spring  hanger 

P74P 

Spring  stud 

Screwed  and  riveted  to  inside  of  case. 

P74C 

studs. : . . ::.:.... 

Fasten  magneto  to  base. 

P74D 

do 

Connect  base  to  case. 

P76A 

Terminal  end  bracket 

Secured  to  terminal  end  of  magneto. 

T96EA... 

Terminal  tube,  complete 

Screwed  into  base. 

P75H 

Washer 

For  lever-catch  pin. 

P75K 

do 

For  spring  hanger. 

P76Q 

do 

For  intermediate  shaft. 

War  Department, 

Office  of  the  Chief  of  Ordnance, 

Washington,  March  10,  1917. 


Form  No.  1814. 
Ed.  Aug.  27-17—500. 


NOU/SOd    SIHl  Nl  SI  d3A31   N3HN^ 
a39\/0N3  Xnnj  HJ.33J.  HOimO  HJ.IM  IVlNOZiyOH  39  01  3ynivu/ijv- 


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Ca^ord  Bros. 

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Syracuse,  N.  Y. 

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